create table dbo.T1
(
keycol INT NOT NULL PRIMARY KEY,
col1 INT NOT NULL,
col2 varchar(max) NOT NULL
)

BEGIN TRAN
INSERT INTO dbo.T1
SELECT 1, 101, 'A'
UNION ALL
SELECT 2, 102, 'B'
UNION ALL
SELECT 3, 103, 'C'
COMMIT TRAN

create table dbo.T2
(
keycol INT NOT NULL PRIMARY KEY,
col1 INT NOT NULL,
col2 varchar(max) NOT NULL
)

BEGIN TRAN
INSERT INTO dbo.T2
SELECT 1, 201, 'X'
UNION ALL
SELECT 2, 202, 'Y'
UNION ALL
SELECT 3, 203, 'Z'
COMMIT TRAN

=====================

--polaczenie1
BEGIN TRAN
	UPDATE dbo.T1 SET col2 = col2 + 'A' WHERE col1 = 101
	
	SELECT col2 FROM dbo.T2 WHERE col1 = 201
COMMIT TRAN

--polaczenie2
BEGIN TRAN
	UPDATE dbo.T2 SET col2 = col2 + 'B' WHERE col1 = 203
	
	SELECT col2 FROM dbo.T1 WHERE col1 = 103
COMMIT TRAN